14.4 ... However, Exploitation from an undefended Breakthrough hex is not allowed if the Breakthrough hex is adjacent to an enemy ground unit, or if a supply line cannot be traced to it at the moment of combat.

If so, then often times it's better not to defend the beach hex but to defend adjacent to it. But I guess the rule's pretty clear on this?

In particular there is a DQB item which asks if units landing on a vacant beach hex can attack adjacent enemy units. The answer is that they can do so only by exploitation, which implicitly assumes the exception Doug has pointed out.

14.4 Breakthrough and Exploitation may occur without a defender being eliminated from the Breakthrough hex anytime a player with a supplied armor unit which has not attacked during that player turn declares his intention to attack a vacant enemy controlled hex with that armor unit (and any other units adjacent to the attacked hex which have not yet attacked in that turn and wish to be included in the attack). The attacking armor unit is moved into the attacked enemy hex and thereby creates a Breakthrough hex from where other armor units may exploit as per 14.32. Units may attack a vacant hex in this manner so as to advance into it as a result of the non-contested combat only if an armor unit is involved in the attack and will occupy the attacked hex (EXCEPTION: 29.436). However, Exploitation from an undefended Breakthrough hex is not allowed if the Breakthrough hex is adjacent to an enemy ground unit, or if a supply line cannot be traced to it at the moment of combat.

DQB: Note, I was wrong in the other thread. Supply fleets must be specified.

Quote:

DQB (& 29.436) Can units which have invaded an undefended beach, attack units adjacent to the beach in the same turn?

A. Units eligible for exploitation can; others cannot.

DQB Must the attacker designate a supply fleet to provide supply to an undefended beach hex when he plans to invade then exploit from it during the Combat Phase?

A. Yes. Similarly, SR has to be over supplied, controlled hexes. So, if you drop a paratroops unit on Great Yarmouth, for example, you must have had a fleet predesignated in order to SR units thence.

DQB Exactly what is a vacant hex?

A. A hex without a defending ground unit; an airbase, air or naval unit does not disqualify it as a vacant hex.

Rule 29.436

Quote:

29.436 If the Invasion succeeds (at least one initially invading ground unit surviving and landing), a Bridgehead counter may be placed. Ground units aboard the Invasion fleet which did not participate in the attack may also be placed on the Bridgehead, up to the five-unit stacking limit. If the target hex contained no enemy ground units, success is automatic and a Bridgehead counter may be placed (but not if the target hex was already controlled by attacker‘s side). Invading units may not attack enemy units adjacent to the target hex, except by Exploitation attack. (In such case one armored unit would have to attack the undefended beach to establish a Breakthrough hex and would be ineligible to Exploit).